One arrangement for multiplexing speech signals and nonspeech signals includes apparatus for transmitting speech signals in one portion of the frequency spectrum of a communication path linking a transmitter and a receiver with the remainder of the bandwidth for transmitting nonspeech signals.
Another; disclosed in U.S. Pat. No. 3,304,372, issued Feb. 14, 1967 and entitled "Voice-Data Multiplexing System for Transmitting Data During Pauses in the Voice Signals"; includes an arrangement for detecting intervals of no speech on the communication path and for inserting a data signal therein. More specifically, at the transmitter, a decision circuit continually monitors an input line. On the one hand, when speech signals are detected on the line, the decision circuit provides a first gating signal to allow passage of the speech signals through a voice gate onto the communication path. On the other hand, when a gap in the speech signals is detected and the gap exceeds a predetermined minimum time duration, the decision circuit provides a second gating signal to allow passage of data signals through a data gate onto the communication path. Between gaps of no speech, data signals are queued for transmission. At the receiver, a first detector monitors signals on the communication path for the appearance of a unique signal which heralds the arrival of speech signals. Also, a second detector monitors signals on the communication path for the appearance of another condition which heralds the arrival of data signals. Thereby the arrangement multiplexes data signals during gaps in voice signals.
Still another; disclosed in U.S. Pat. No. 3,406,344, issued Oct. 15, 1968 and entitled "Transmission of Low Frequency Signals by Modulation of Voice Carrier"; includes an arrangement wherein speech signals are modulated by low frequency data signals. The modulated speech signals, the speech signals being the carrier signals, are transmitted over the communication path to the receiver. At the receiver, an envelope detector may be used to recover the data signals from the modulated speech signals. Also, the speech signals may be readily reproduced.
Unfortunately, users of known arrangements for (de)multiplexing speech signals and nonspeech signals experience excessive distortion or perceive others as encroaching on the communication path.